Developmental morphology and systematics of Trematocarpus dichotomus (Sarcodiaceae, Rhodophyta) from Chile

Abstract

Rodríguez-Prieto C. and Hommersand M.H. 2012. Developmental morphology and systematics of Trematocarpus dichotomus (Sarcodiaceae, Rhodophyta) from Chile. Phycologia 51: 586–595. DOI: 10.2216/11-122.1Trematocarpus dichotomus, the generitype of Trematocarpus Kützing, was restricted to the Pacific coast of South America from southern Peru to Chiloé in south-central Chile. Our investigation established that the vegetative thallus consists of an outer and inner cortex that encircles a medulla of uniformly separated, cylindrical to compressed filaments cross-linked by secondary pit connections. Spermatia were initially cleaved singly and released from the tip of an elongated spermatangium and later sequentially from a series of developing spermatia that matured basipetally within the spermatangium. Carpogonial branches were three-celled, initially directed outwardly but then curving sharply inwardly, the carpogonium producing an abruptly reflexed trichogyne. A single transverse division of the carpogonium after fertilization resulted in a proximal cell that fused with the first cell of the carpogonial branch, which became the generative auxiliary cell. The auxiliary cell cut off a single gonimoblast initial towards the thallus surface that branched beginning at the three-celled stage, with the cells in adjacent branches linking laterally by secondary pit connections. Surface cortical cells grew and branched to form a pericarp that split into inner and outer pericarp layers separated by a central cavity. Gonimoblast filaments were initially surrounded by inner pericarp from which they grew into the cavity and bore carposporangia terminally in branched chains. The gonimoblast filaments fused lengthwise progressively as they grew, and adjacent filaments linked laterally by secondary pit connections to form a fusion network referred to as the ‘gonimoblast reticulum’. Inner cells of the gonimoblast reticulum fused with cells of the inner pericarp, uniting the carposporophyte with the gametophyte through a basal placenta. Carposporangia may germinate in situ inside the cystocarp. Tetrasporangia were formed successively in nemathecia from elongated tetrasporangial initials on the concave sides of branches and were zonately divided. Several developmental stages documented here are newly reported for Trematocarpus and the family Sarcodiaceae.